1. Field of the Invention
This invention relates to a lens centering mechanism for centering a lens when a lens holding member holding a lens is mounted to a main body unit of a lens barrel, a lens apparatus, and to an imaging apparatus having such lens centering mechanism.
2. Description of Related Art
Up to now, there have been used lens apparatus in which an image of an object is formed by plural lenses arranged in a main body unit of the lens barrel as optical axes thereof are aligned with one another. There have also been used imaging apparatus, such as a digital still camera or a digital video camera, for receiving an image of an object, formed by such lens apparatus, by a solid-state imaging device, such as a CCD (charge-coupled device) or CMOS (complementary metal-oxide semiconductor) device, and for outputting electrical signals, obtained on photo-electric conversion of light received by the solid-state imaging device, in order to generate digital image data corresponding to the object image.
Among the lens apparatus, there is such an apparatus in which certain ones of plural lenses, arranged in the main body unit of the lens barrel, are held by a lens holding member, and in which there is provided a lens centering mechanism for centering the lenses when the lens holding member is mounted to the main body unit of the lens barrel (see for example References Cited 1 to 3).
For example, a lens apparatus 200, shown in FIG. 1, is provided with a lens centering mechanism in which, when mounting a lens holding member 202 on the front side of a main body unit of the lens barrel 201, a plural number of plate springs 205 and coil springs, not shown, are interposed between a corresponding plural number of tapped holes 203, provided in a mounting surface of a main body unit of the lens barrel 201, and a corresponding plural number of through-holes 204, provided in a mounting surface of the lens holding member 202, and a plural number of set screws 206 are inserted in the tapped holes 203, through the through-holes 204 and the plate springs 205, from the front surface of the lens holding member 202, with the tightening of the set screws 206 being then adjusted to adjust the tilt of a lens 207 held by the lens holding member 202.
On the other hand, a lens apparatus 300, shown in FIG. 24, is provided with a lens centering mechanism in which a toroidally-shaped plate spring 303 is secured to a main body unit of the lens barrel 301, a plural number of guide projections 307, provided to the outer rim of a lens holding member 306, are engaged in a corresponding plural number of guide holes formed in the outer rim of a lens holding member 306, and in which, as the lens holding member 306 is held by the plate spring 303, a corresponding plural number of adjustment screws 309 are tightened in a corresponding plural number of tapped holes 308 formed in the front surface of the lens holding member 306 to cause the adjustment screws 309 to be variably protruded towards the plate springs 303 to adjust the tilt of a lens 310 held by the lens holding member 306. On the outer rim of the lens holding member 306, there is provided a sealant rubber piece 302 for prohibiting intrusion of dust and dirt from outside.    Reference Cited 1: Japanese Laying-Open Patent Publication H11-160749.    Reference Cited 2: Japanese Laying-Open Patent Publication H2-113214.    Reference Cited 3: Japanese Laying-Open Patent Publication 2002-196205.
However, with the above-described lens apparatus 200 and 300, the lens centering mechanism takes up relatively large space portions on the outer rim of the main body unit of the lens barrel and the lens holding member. In particular, on the front surface side of the main body unit of the lens barrel, the outer shape of the main body unit of the lens barrel is significantly swollen out with respect to the lens held by the lens holding member, thus leading to a significant demerit in reducing the overall size of the apparatus.
With the above-described lens apparatus 200, 300, the tilt of the lens, held by the lens holding member, is adjusted as an image of a chart is formed on a CCD and, as the image of the chart, picked up by the CCD, is observed on a monitor. However, with these lens apparatus 200, 300, in which the set screws or adjustment screws are tightened in a direction parallel to the optical axis, from a position proximate to the front side lens of the lens holding member, an image of a jig for tightening the screws or the operator=s hand tends to be taken into an image of the chart at the time of adjustment, thus obstructing the centering operation.
On the other hand, with the above-described lens apparatus 200, 300, in which the set screws or the adjustment screws are mounted in a direction towards the optical axis, at the time of adjustment, these screws tend to be intruded into the inside of the main body unit of the lens barrel, thus giving rise to a risk of the image of the component parts being taken into the chart image. Moreover, with the above-described lens apparatus 300, the adjustment screws 309 for adjusting the tilt of the lens 310 is needed in addition to the set screws 304, thus increasing the number of the component parts.
On the other hand, if, as described in the Reference Cited 1, the lens tilt is adjusted as offset pins provided at two outer peripheral points are rotated, with a reference pin provided at a point on the outer rim as a fulcrum point, the lens is displaced in its entirety in a direction towards the optical axis, thus possibly affecting the optical performance. In addition, with the offset pins fitted in elongated holes, it is necessary to provide a clearance, from the aspect of designing, with the result that the overall lens may possibly suffer from backlash.
If, as described in the above Reference Cited 2, the movable lens barrel is to be moved by a conjoint operation of a guide groove formed in a guide tube, a cam groove formed in a cam cylinder and a cam pin provided at a point of intersection of the guide groove and the cam groove, the cam pin is fixedly threaded to the movable lens barrel, thus leading to significant demerit in reducing the number of component parts and the number of operating steps. On the other hand, the tilt of the lens held by the movable lens barrel is adjusted by rotating the cam pin about a center axis of a second radial portion fitted in the guide groove and in the cam groove and which is offset relative to the first radial portion. In this case, at least two portions of the guide groove and the cam groove need to be fitted in order to hold the second radial portion of the cam pin operating as reference for tilt adjustment. Moreover, there is no limitation imposed on the rotation about the optical axis of the movable lens barrel, thus giving rise to a risk that the lens not only tends to be shifted along the optical axis but also tends to be rotated about its optical axis. There is also a risk that, except if the cam pin is fixed after adjustment, the cam pin tends to be rotated during use such that it becomes impossible to maintain the adjusted state.
On the other hand, if a spring washer, as a member responsible for biasing a lens holding frame, is mounted in the form of a flange, that is so that the spring washer is larger in diameter than the outer rim of the lens holding frame, as in the case of the Reference Cited 3, the overall apparatus cannot readily be reduced in size. Additionally, the number of component parts is increased because a thrusting mechanism for thrusting the spring washer by a screw and an adjustment mechanism by the offset pins are separated from each other.